A major challenge in biomedical research is to understand the functional interplay between gene regulation, chromosome structure, chromatin modifications, and human disease. X-chromosome dosage compensation (DC) in the nematode C. elegans is exemplary for such analysis for the following reasons: DC is mediated by a condensin complex, a chromosome restructuring complex essential for chromosome segregation; DC is essential for proper gene expression and viability because it distinguishes X chromosome from autosomes to control hundreds of genes on X simultaneously; and X-chromosome-specific chromatin modifications are essential for DC. The dosage compensation complex (DCC) binds selectively to X chromosomes of XX embryos to reduce transcription by half, thereby equalizing X-chromosome transcription between XX and XO embryos. Our recent experiments indicate that the DCC imposes a unique spatial organization onto the X chromosomes of XX embryos by binding to its highest affinity recruitment sites on X (rex sites). Mutations that disrupt DCC binding disrupt that X-specific conformation. Proposed experiments extend this analysis and explore the relationship between chromosome structure and gene expression by using our highly efficient genome editing strategies to delete and insert rex sites on X and autosomes and then assess the consequent changes in chromosome conformation and gene expression. Our study is unique in providing a robust example of a major change in chromosome structure imposed by a specific complex, on a specific chromosome, through high- affinity binding to its targets. We have also shown recently that a DCC subunit has a demethylase activity that is responsible for the selective enrichment of H4K20me1 on X chromosomes of XX embryos upon DCC binding. Selective mutation of the catalytic residues abrogates H4K20me1 enrichment and disrupts dosage compensation. These highly specific mutations allow us to test, in an unusually precise way, the role of histone modifications in X-chromosome structure and gene expression. H4K20me1 is also enriched on the mammalian inactive X chromosome, but the role of this enrichment in transcriptional silencing is not known, nor is a selective reagent available to test its role. Changes in histone lysine methylation states are a common occurrence during tumor formation, and strong correlation now exists between an increase in activity of histone demethylases and tumor progression. Hence, our studies of a chromosome-specific demethylase enzyme may become directly relevant to human health. Lastly, we have gained an evolutionary perspective on the X-chromosome DNA sequences that recruit DCC complexes to X chromosomes of highly diverged nematode species. Surpisingly, while the DCC complexes are conserved, the cis-acting motifs are highly diverged. More typically, the target site specificity of conserved regulatory proteins that control multiple celluar processes by targeting hundreds of sites is far more evolutionarily constrained. Hence, the divergence in DCC binding specificity provides an unusual opportunity to understand the path for a concerted change in hundreds of target sites.